1. Field of the Invention
The present invention relates to a system for supplying operating voltage to a center processing unit (CPU), and particularly to a system for supplying operating voltage to a CPU which is not affected by surrounding temperature of a motherboard.
2. General Background
A CPU is the most important component in a computer as a control center for controlling operation of the computer. When the computer begins to run, the CPU reads data from a memory, and computes a plurality of results bases on the data, then transmits the results to the memory. Also, the CPU controls a motherboard to communicate with external devices for receiving data outside the computer.
Like other electronic components on a motherboard, the CPU must work with an operating voltage which is supplied by the motherboard. Because deferent kinds of CPUs have deferent operating voltages, so a particular power supply circuit is set on the motherboard for supplying an operating voltage suits for the CPU. FIG. 2 shows a power supply circuit for supplying an operating voltage to the CPU. The power supply circuit converts direct current (DC) voltage supplied by a power supply of the computer to an operating voltage suitable for the CPU. The power supply circuit includes a Pulse Width Modulation (PWM) controller. An output terminal of the PWM controller is connected to a feedback circuit. The PWM controller outputs an output voltage to the feedback circuit via the output terminal, and receives a feedback voltage from the feedback circuit. The PWM controller compares the feedback voltage with a reference voltage, and converts the output voltage to a suitable voltage for the CPU.
Conventionally, the feedback circuit includes a plurality of resistors. When the computer is running, surrounding temperature of the motherboard increases due to thermal affect of current. The increasing of temperature causes resistance of the resistors to change. The feedback voltage passes through the resistors, and changes due to the changing of resistance of resistors. The PWM controller receives an inexact feedback voltage, and can't control the output voltage correctly. So the CPU is operating on an incorrect voltage.
What is needed is a system for supplying operating voltage to a CPU which is not affected by surrounding temperature of a motherboard.